Reciprocating drive mechanisms have found considerable utility in oil well pumps since they can provide the required reciprocating pumping action with varying stroke length and speed. Typically, these reciprocating drive mechanisms comprise a rotating prime mover in the form of an internal combustion engine, a pinion rotated by the prime mover, a closed loop rack gear meshing with the pinion, and a drum coupled to the rack gear. From the drum, a cable extends to a polish rod and sucker rod used to pump the oil from the well. As is known, the pinion and rack gear combination converts the rotary motion from the prime mover into a reciprocating motion to reciprocate the polish and sucker rods.
One example of a recently developed reciprocating drive mechanism is disclosed in commonly assigned pending application Ser. No. 415,478, filed Sept. 7, 1982 in the name of Robert J. Smith and entitled Well Pumping Unit. This application discloses such a pinion and rack gear conversion system; however, this system has difficulties accomplishing the required reciprocating motion under heavy loads. Thus, it is typical to use a polish rod that weighs about 13,000 pounds and to have the entire polish and sucker rod system under loads that are greater than 50,000 pounds and can actually reach a million pounds. Under these loads, it has been found that the pinion tends to dig into the rack when rotation of the pinion is attempted and the pinion actually tries to move itself rather than the rack. In addition, the shaft holding the pinion actually tends to bend as the pinion tries to walk along the stationary rack.
Other examples of pinion and rack gear reciprocating mechanisms are disclosed in the following U.S. Patents: U.S. Pat. Nos. 264,483 to Smith; 579,559 to Bossert; 1,119,965 to Kelly; 1,211,221 to Pfeiffer; 1,598,553 to Butler; 1,611,914 to Jenkins; 2,091,287 to Leonard; 2,136,478 to Travis; 2,170,313 to Whittlesey; 2,200,292 to Patterson; and 2,732,722 to Wilshusen.
While these patents do disclose reciprocating drive mechanisms, typically they do not provide a pause or relaxation between the reciprocating movements, they cannot handle heavy loads, they are subject to significant wear patterns, and they are complicated to manufacture and have limited durability.